为什么我必须单击两次才能滚动?Scrollable Label in kivy， python.

Question

我有以下问题：我需要编写一个应用程序，我将为每个问题显示正确的答案。我用kivy编写了一些代码，我正在为一件事而苦苦挣扎。我创建了一个页面。有一个用于显示答案的按钮，但是按一下后，我只能看到部分答案，无法滚动。但是，当我第二次按下按钮时，一切都很好。你能告诉我这是为什么吗？怎么修？我想在按下按钮一次后查看所有答案并能够滚动。

import kivy
from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.gridlayout import GridLayout
from kivy.uix.button import Button
from kivy.uix.screenmanager import Screen, ScreenManager
from kivy.uix.scrollview import ScrollView
from kivy.uix.boxlayout import BoxLayout
from kivy.core.window import Window
from kivy.config import Config
Config.set('graphics', 'resizable', True)
import os
import sys
class MyApp(App):
def build(self):
self.screen_manager = ScreenManager()
self.answers = Answers()
screen = Screen(name = "Answers")
screen.add_widget(self.answers)
self.screen_manager.add_widget(screen)
return self.screen_manager
class Answers(GridLayout):
def __init__(self, **kwargs):
super().__init__(**kwargs)
self.rows = 3
self.label = Label(text = "Answers: ", font_size = 40)
self.add_widget(self.label)
self.button = Button(text="Show answers")
self.button.bind(on_press=self.showanswers)
self.add_widget(self.button)
self.scroll = ScrollableLabel(height = Window.size[1]*0.75, size_hint_y = None)
self.add_widget(self.scroll)

def showanswers(self, instance):
f = open("text.txt", "r")
lines = f.readlines()
ScrollableLabel.update(self.scroll, lines)
myapp.screen_manager.current = "Answers"

class ScrollableLabel(ScrollView):
def __init__(self, **kwargs):
super().__init__(**kwargs)
self.layout = GridLayout(cols = 1,  size_hint_y = None)
self.add_widget(self.layout)
self.lines = Label(size_hint_x = 1, size_hint_y = None, text_size = (self.width, None))
self.scroll_to_point = Label()
self.scroll_to_point.bind(texture_size=self.scroll_to_point.setter('size'))
self.layout.add_widget(self.lines)
self.layout.add_widget(self.scroll_to_point)

def update(self, lines):
self.lines.text = 'n'
for i in range(len(lines)):
self.lines.text += 'n ' +str(i+1) + ". " + lines[i]
self.layout.height = self.lines.texture_size[1]
self.lines.height = self.lines.texture_size[1]
self.lines.text_size = (self.lines.width*0.75, None)
self.scroll_to(self.scroll_to_point)
f = open("text.txt", 'a+')
for i in range(30):
f.write("Important text n")
f.close()
myapp = MyApp()
myapp.run()

Answer 1

我认为您的小部件高度没有正确更新，要纠正这一点需要做一些绑定。由于"kv"语言会自动进行绑定，因此我提供了一个使用"kv"的答案：

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.label import Label
from kivy.uix.gridlayout import GridLayout
from kivy.uix.button import Button
from kivy.uix.screenmanager import Screen, ScreenManager
from kivy.uix.scrollview import ScrollView
from kivy.core.window import Window
from kivy.config import Config
Config.set('graphics', 'resizable', True)
class MyApp(App):
def build(self):
self.screen_manager = ScreenManager()
self.answers = Answers()
screen = Screen(name = "Answers")
screen.add_widget(self.answers)
self.screen_manager.add_widget(screen)
return self.screen_manager
class Answers(GridLayout):
def __init__(self, **kwargs):
super().__init__(**kwargs)
self.rows = 3
self.label = Label(text = "Answers: ", font_size = 40)
self.add_widget(self.label)
self.button = Button(text="Show answers")
self.button.bind(on_press=self.showanswers)
self.add_widget(self.button)
self.scroll = ScrollableLabel(height = Window.size[1]*0.75, size_hint_y = None)
self.add_widget(self.scroll)

def showanswers(self, instance):
f = open("text.txt", "r")
lines = f.readlines()
self.scroll.update(lines)
myapp.screen_manager.current = "Answers"

class ScrollableLabel(ScrollView):
def update(self, lines):
self.ids.lines.text = 'n'
for i in range(len(lines)):
self.ids.lines.text += 'n ' +str(i+1) + ". " + lines[i]
Builder.load_string('''
<ScrollableLabel>:
size_hint_y: None
GridLayout:
cols: 1
size_hint_y: None
height: self.minimum_height  # adjust height to handle the Label
Label:
id: lines
size_hint_y: None
height: self.texture_size[1]  # set height based on text
''')
f = open("text.txt", 'a+')
for i in range(30):
f.write("Important text n")
f.close()
myapp = MyApp()
myapp.run()

我认为size_hint_y: None的两个实例和相应的height规则是关键。

请注意，我还更改了：

ScrollableLabel.update(self.scroll, lines)

自：

self.scroll.update(lines)